Mo, K.C. and Lettenmaier, D.P.
2018
"Drought variability and trends
over the central United States
in the instrumental record."
Journal of Hydrometeorology 19:
1149-1166.
SUMMARY:
Climate models predict
extreme weather events
will become more frequent,
and more severe, in the future,
in response to CO2-induced
global warming.
I disagree -- in reality,
warming of the Arctic
has reduced the
temperature differential
between the tropics
and the Arctic, making
Northern Hemisphere
weather milder.
Claims that extreme
events, such as droughts,
were caused by man made
climate change,
can be refuted
by identifying similar events
when CO2 levels were
significantly lower,
and climate change
was considered to have
natural causes.
Climate model projections
of more frequent and more
severe drought events
are not true for the
contiguous 48 states.
The frequency
and magnitude
of US droughts
are not increasing
-- they have decreased
over the past century.
DETAILS:
Mo and Lettenmaier (2018)
referenced a widespread
and severe drought in 2012
that covered more than 62%
of the contiguous US,
and caused $40 billion
in damages.
They investigated
the 2012 US drought
event in the context
of the past century,
seeking to determine
if such events
are becoming
more frequent,
or more severe.
Mo and Lettenmaier used
"gridded observed precipitation
and reconstructed total moisture
percentiles and runoff from
four land surface models"
to develop an integrated
drought index (IDI) for defining
drought in the continental USA
over the period 1916-2013.
Using this index, drought periods
were then defined as having
an IDI value less than 0.3.
Mo and Lettenmaier filtered the data
to examine severe drought events
that covered 50% of the continental US
for a period of six months or longer.
Analyses of these data revealed:
(1)
Severe drought events
were mainly located
in the central U.S.,
(2)
"the 2012 drought event
was not unique,"
considering that there were
"16 great drought events
in the 98 years of record
[they] analyzed,"
(3)
"great droughts occurred less often,
and events were less severe
as time progressed" and
(4)
all but two of the 16
great drought events
occurred in the first half
of the record.
Mo and Lettenmaier detected
a relationship between the
Atlantic Multidecadal Oscillation (AMO)
and drought (there was a higher
percentage of drought when the AMO
was in a positive phase) and between
ENSO and drought (12 of the 16 great
drought events occurred during cold
La Niña years).
But ... droughts did not always occur
when the AMO was in a positive phase
or when La Niña conditions existed.
